One of the most common questions and requests we receive after carrying out an In Vitro Fertilisation cycle is the following: how many embryos should I transfer? One or two? In this post we will analyse all the pros and cons of transferring a single embryo versus transferring two embryos (1). According to the data available at a European level during 2019, 56% of single embryo transfers were carried out and 41% of two-embryo transfers. In our country, according to data from the Spanish Fertility Society (SEF), in 2021, 65% of single transfers and 35% of two-embryo transfers were performed.
What factors should be considered when deciding on embryo transfer?
Effectiveness
The effectiveness of carrying out two single-embryo transfers compared to a single one, in terms of live birth, is similar.
Safety
Multiple pregnancies carry a higher obstetric risk, increasing the incidence of: caesarean section, gestational diabetes, hypertension, pre-eclampsia, placental abruption, placenta praevia, and postpartum haemorrhage. There are also more risks for newborns: increased risk of prematurity, congenital malformation, low birth weight, ICU admission and mortality. Not all two-embryo transfers lead to a twin pregnancy, but even in these cases where only one embryo ultimately develops, there are also more risks: higher risk of congenital malformations, low birth weight, preterm birth, or neonatal death (2,3).
Costs
Direct costs are higher in multiple pregnancies, as they require more visits, a greater number of procedures, medication, and surgery. Indirect costs are also higher, in terms of sick leave, travel for treatments, and the need for support units and networks.
Mental health of families with twin births
Parents of twins experience a higher incidence of postpartum depression during the first four years of life, negative effects on their relationship as a couple, parental stress, feelings of incompetence as a mother or father, and even the development of hostile reactions towards the children. As for the children, there are no differences between twins and singleton pregnancies during the first years of life, but between ages 6 and 12, twins show less formation of trusting bonds with their environment, less emotional communication with their parents, less ability to recognise mistakes, less initiative, and are less proactive. The final decision about the number of embryos to transfer must be agreed upon, but most couples, once they know the real risks that a two-embryo transfer can carry, opt for a single embryo transfer.
Scientific societies recommend single embryo transfer, regardless of the patient’s age, whether she has low ovarian reserve, whether the eggs are her own or donated, and whether the embryos are fresh or frozen: the risks will always be lower and the success rates comparable. For all these reasons, at our centre, for over 15 years now, we have recommended single embryo transfer, since our goal is to help make every woman’s dream come true: becoming the mother of a healthy newborn.
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Bibliography
- ESHRE Guideline Group. 2023. Available at: https://www.eshre.eu/Guidelines-and-Legal/Guidelines/Guidelines-in-development/Embryo-transfer
- Eapen A, Ryan GL, Ten Eyck P, Van Voorhis BJ. Current evidence supporting a goal of singletons: a review of maternal and perinatal outcomes associated with twin versus singleton pregnancies after in vitro fertilization and intracytoplasmic sperm injection. Fertil Steril. 2020;114:690-714.
- Rodriguez-Wallberg KA, Veleva Z. Higher obstetric and perinatal risks for twins and the need for single embryo transfers in assisted reproduction. Acta Obstet Gynecol Scand. 2023;102:968-969. doi:10.1111/aogs.14639.
